This invention pertains generally to infrared (IR) seekers and particularly to an IR seeker intended for use as a guidance apparatus within a cannon launched guided projectile.
A guidance system for a spinning projectile is described in U.S. Pat. No. 4,347,996, issued Sep. 7, 1982 to V. A. Grosso and assigned to the same assignee as this application.
An IR, high G hardened, strapped-down seeker intended for use as the sensor in a cannon-launched spin-stabilized guided missile is described in U.S. Pat. No. 4,690,351, issued Sep. 1, 1987 to R. A. Beckerleg, et al. (which patent is assigned to the same assignee as this application and is incorporated herein by reference). In U.S. Pat. No. 4,690,351, a strapped-down IR seeker is described comprising a catadioptric optical telescope that is fixed to the body of the projectile but whose optical axis is inclined at an angle; e.g. 6.degree., with respect to the centerline of the projectile. The spin of the projectile is utilized to scan an annular ring of the target area. An optical wedge (a small angle prism) serves as the IR dome during the terminal phase of flight. The wedge is rotated .+-.90.degree. about the projectile spin axis to steer the seeker line-of-sight, LOS, radially from the projectile centerline to twice the fixed off-axis optical angle; e.g., 12.degree.. The steering by wedge rotation performs the gimbaling function. Thus, the projectile spin motion scans a circular annular pattern and the radius of the pattern is varied by controlling the position of the rotating optical wedge. The resultant pattern for discrete wedge rotation angles is a series of concentric annuli. For linear wedge rotation a spiral search pattern is generated. The position of the servo in the wedge is controlled by a data processor. The processor first generates the seeker search commands. Once a target is detected, the wedge position is commanded to the next expected radial position and a track mode commences. In the track mode, target line-of-sight measurements are made by differencing sequential line-of-sight positions to generate a line-of-sight rate output for the target. To provide adequate optical wedge strength during high G induced loads, the wedge is prestressed by a metal band or ring. A controlled shrink fit method of application is used. The steering of the LOS by the wedge allows a light weight and small field of view telescope to be used to cover the complete search and track area and only a few optical infrared detectors are required.
Although such a strapped-down IR seeker is useful in many applications, the seeker has some limitations. For example, the seeker can only be used on a rapidly spinning projectile. Additionally, the data rate is a variable and becomes excessive at high spin rates and large off boresight error angles.